A patch antenna formed on a dielectric substrate is used for a radar or the like provided in a mobile body such as a vehicle or an airplane to monitor surroundings thereof. The patch antenna is provided with a radiating element including a patch-like pattern formed on one surface of the dielectric substrate and a base plate formed on the other surface of the substrate.
If the patch antenna is used as an antenna for an on-vehicle radar apparatus, for example, the patch antenna may be mounted in a bumper of the vehicle. In this case, it is known that, a portion of a radio wave radiated from the antenna is reflected at an inner wall of the bumper and further re-reflected at a radiating surface of the antenna, and the re-reflected wave interferes with the radiated wave and affects radiation characteristics of the antenna.
PTL 1 listed below discloses an electromagnetic-wave reflecting surface of a planar substrate structure including a substrate having a base plate formed on one surface thereof and a plurality of conductor patches and connection elements all provided on the other surface of the substrate. The conductor patches are arrayed at predetermined intervals and the connection elements electrically connect the conductor patches together. The use of the electromagnetic-wave reflecting surface allows a wave front of a reflected wave reflected at the electromagnetic-wave reflecting surface to be inclined. This inclination of the reflected wave is achieved by configuring the connection elements based on an increase or decrease in the capacitance or the inductance, according to an arranged position of the conductor patches along one desired direction. That is, reflection of an electromagnetic wave can be oriented to a desired direction.